But implants that can stay in the brain for long periods of time, still face one huge hurdle: the human body doesn't like them.

There are a few ways brain implants are embedded, all involving invasive surgery. Surgeons drill small holes through the skull and "insert long thin electrodes — like pencil leads — until they reach their destinations deep inside the brain," according to a 2012 article in The Scientist. The wires extend outside the head and attach to the external recording device that does the computing work.

Implants can record activity from a group of neural cells, electrically stimulate cells to start processes like movement, or block electric signals that would cause abnormal movement, as in the treatment of Parkinson's Disease. They're often made of stainless steel or other types of metal — useful for conducting electric signals, but problematic for biological purposes.

"If you look at implanted electronics in the brain over the past 10 to 20 years, all suffer from a common problem which is the implant's electronic probes ... create scarring in brain tissue," said Charles Lieber, a chemist from Harvard University who is working on a tiny mesh brain implant.

When the body senses an implant made of material that triggers the body's immune system, glial cells begin to create scar tissue around it to protect the brain from what it considers a foreign body. When a probe becomes too engulfed in glial scarring, it loses functionality.

"You can think about it as putting an insulator on it that prevents it from interacting with the neurons," Lieber said.

Brain implants generally target a specific group of neurons. But brain tissue often moves around inside the skull, potentially causing implants to slip from their targeted spots, lose contact with the neurons, and become ineffective. This slippage can also cause more scarring.

To address this mismatch, implants are getting smaller and looking less like the electronic devices that we're familiar with and more like the structure of the brain itself. Lieber's flexible mesh implant, recently published in the journal Nature Nanotechnology, is made of biocompatible material that limits scarring and was able to work for five weeks after being injected into a lab mouse's brain. Lieber said his lab is now doing extended testing to find out how long the implant can remain without setting off the immune system's alarms.

The mesh implant unfurls in the brain after injection. Lieber Research Group, Harvard University "We're up to three months so far in this ongoing study," he said. "There's been no change in the response and it still has good recording behavior, unlike other devices where they either lose the signal or there is so much scarring over time that you have to move the implant's position."

Other developments include "neural dust," sensors about the thickness of a single human hair that can be peppered onto the brain. These wireless implants, in development by a team at the University of California, Berkeley, "convert electrical signals into ultrasound that could be read outside the brain" by receivers attached to the skull, according to the Wall Street Journal.

Scientists are still looking for the perfect balance between an implant that the body won't reject and strong enough to actually do the computing necessary for complex applications. The faster they come to a breakthrough, the more common brain implants will become, and the more likely people will use them for enhancement.